Waste Processing

ABSTRACT

An apparatus for processing material ( 29 ) such as organically coated waste and organic materials including biomass, industrial waste, municipal solid waste and sludge is provided. The apparatus comprises an oven having a rotatable portion comprising a treatment chamber adapted to receive material for treatment. A plurality of gas inlets are provided in at least one wall of the treatment chamber through which hot gasses are introduced to the treatment chamber to heat the material therein so as to cause the organic components thereof to pyrolyse or gassify. At least one retarder means ( 26 ) is located in the treatment chamber to retard the movement of waste material therein as the oven rotates.

The present invention relates to improvements in the processing of materials having an organic component. In particular the method relates to improvements in the processing of such materials in rotating ovens.

The use of large rotating ovens for processing waste is known in the prior art. Examples of rotating ovens for such use can be found, for example, in PCT publication WO2004/059229. This document discloses a rotating oven for processing waste which has a plurality of nozzles for omitting heated gas into the processing chamber thereof. Although only a single row of inlets is shown in this prior art document, in practice an array of inlets covering the sides of the processing chamber, or at least one side thereof, can be provided.

As the oven rotates scrap material therein will fall over the inlets temporarily blocking them and reducing the gas flow therethrough. In reality when operating such a system as the material moves in the processing chamber as the oven is rotated it tends to move from one side to the other of the oven substantially as a single bulk movement i.e. once the stiction between the material to be processed and the surface it is resting on is overcome by the angle of the up and reaching a particular degree the entire mass of material will slide down that side of the oven and then substantially stop until the oven is further rotated so that the material once again overcomes its stiction. This is especially the case in processing chambers having at least one flat side as opposed to circular or tubular ovens. In circular or tubular ovens a constant tumbling of the material is achieved whereas in a flat sided oven the bulk movement of the mass of material as described above occurs. This can be disadvantageous in the speedy processing of waste material as while the material is substantially bunched together only the top and bottom surfaces of the material are exposed to the hot gasses and therefore become heated to react and release gas.

A further problem of the mass movement of material in this way is that, as the material is often quite dense it will tend to block the flow coming out of the nozzles beneath where it is resting. This results in more of the flow entering the processing chamber from nozzles which are not in direct contact with the material to be processed. This is also disadvantageous as the quickest way to transfer heat from the hot gasses into the materials that are being processed is for the hot exhaust gasses to be injected directly into the materials.

A further problem with existing rotating ovens, such as that found in the prior art, is that when an array of gas outlets is provided around the different sides of the oven and, as described above, the quickest way to transfer heat into the material is to directly inject gas into that material, as the material is located on the lower side of the processing chamber, due to gravity, only a small proportion of the inlet nozzles are capable of directly injecting hot gasses into the material being processed. That is, if as described above, the gas flow from these nozzles has not been prevented by the mass of material sitting on top of them.

As described in the prior art, the processing chamber can be a double-walled chamber that has hot gasses passing between an inner and outer wall thereof so as to heat the inner wall. As the materials that are being processed come into contact with this inner wall, then heat is transferred from the exhaust gasses circulating between the two walls into the material by its contact with the hot inner wall. Further, as described above, as the material within the oven tends to move as a single mass, only a small part of the inner wall is in contact with the waste material at any one time, thereby reducing heat transfer efficiency into displaced material.

It is the purpose of the present invention to provide an improved apparatus and method for processing waste that at least partially mitigates some of the above-mentioned problems.

According to a first aspect of the invention there is provided an apparatus for processing material such as organically coated waste and organic materials including: biomass, industrial waste, municipal solid waste and sludge; the apparatus comprising: an oven having a rotatable portion comprising a treatment chamber adapted to receive material for treatment; a plurality of gas inlets in at least one wall of the treatment chamber through which hot gasses are introduced to the treatment chamber to heat the material therein so as to cause the organic components thereof to pyrolyse or gassify; and at least one retarder means located in the treatment chamber to retard the movement of waste material therein as the oven rotates.

Preferably the oven has at least one substantially flat side and the retaining means are provided on the flat side of the oven.

The exact reaction causing the breakdown of the organic material within the processing chamber will depend upon the processing chamber conditions. If there is zero or substantially zero oxygen present in the processing chamber, then the reaction will be predominantly a pyrolysis reaction. Where there is some oxygen present, there will be a gassification which will include some oxidation. In either reaction a gas will be produced that can be used as described in the prior art.

The retarder means to slow the movement of waste material as the oven rotates. Without the retarder means of the invention, an oven having a substantially flat side would rotate until such point that the gravitational forces on the waste material therein overcame the stiction forces resisting movement of that material. Once the stiction forces are overcome then, without the retarder means, the material would move substantially as one solid mass from its current position to a new position substantially at the lowest point of the chamber, sliding across the substantially flat surface. The retarder means slow the movement of the waste material as the oven rotates so that it does not have the same sudden movement as one single mass from one place to another within the chamber but instead moves more gradually. This more gradual movement extends the time period for which the waste material is in contact with the sides of the processing chamber as it passes thereover and increases the surface area of the material being processed. By increasing the surface area of the material being processed, greater heat exchange can take place between the hot gasses and the material.

In a preferred embodiment, the retarder means can be moved between an active position in which they protrude into the treatment chamber and an inactive position wherein they protrude into the treatment chamber by a lesser amount. In their inactive position the retarders may be substantially flush with the walls of the treatment chamber.

The apparatus preferably has an array of retarder means spread about a surface thereof. The retarder means can be moved between their active position and their inactive position to retard the movement of the material within the processing chamber by different amounts as the chamber rotates. By, for example, activating the retarder means in a rippled effect which may be slowly released from this current position to slide down the chamber walls to a new position at the lower-most point of the chamber. By allowing a gradual movement of the material maximum heat exchange into that material can be achieved.

In one preferred embodiment the retarder means are made of spring steel and the retarder means resiliently deform when the retarder means move from its active position to its inactive position. The retarder means may extend through the walls of the treatment chamber and may further comprise actuator means located outside the treatment chamber for actuating the retarder means. This enables the actuators to be maintained in a lower temperature environment whilst still being able to move the retarder means from the active position to the inactive position. The actuator means may, for example, be magnetically driven actuators. In one preferred embodiment the retarder means may comprise a flow path therethrough to enable hot gasses to be introduced into the treatment chamber through the retarder means. In this way, as the retarder means extend from the walls of the chamber, the gas left in the retarder means can be deposited directly into the material being treated as opposed to the prior art systems which only allow heat to be input into the surfaces of the mass of waste being processed.

The treatment chamber may preferably have a double wall, comprising an inner wall and an outer wall extending along at least one of its side and its retarder means may extend through both the inner and the outer walls. In this manner hot gasses can flow between the inner and outer wall thereby heating the surfaces of the treatment chamber. In addition hot gasses can pass through inlets into the interior of the processing chamber and/or alternatively heated gasses can be passed through the flow paths in the retarder means so as to be deposited into the material within the processing chamber. In one preferred embodiment the retarder means each comprise a plurality of inverted hooks arranged in a radial way about a common central axis with the ends of the hooks based from the common central axis. In this way the retarder may resemble palm trees or the framework of an umbrella. The retarder means, in particular the inverted hooks, may each comprise a hollow tube through which hot gas can pass into the treatment chamber preferably with the ends of the inverted hooks are bent so that hot gas emitting from them is directed away from the surface of the treatment chamber. In this way the gas emitting from the ends of the hook shaped retarder means is directed upwards into the mass of waste within the processing chamber. In a preferred embodiment the retarder means can be rotated.

In one embodiment the retarder means may comprise a shaft and a retarder head. The shaft can be pivotally connected to the retarder head. In this manner when the retarder is in its activated position, the head of the retarder can rotate under the influence of gravity as the oven as a whole is rotated. According to a second aspect of the inventions there is provided a method of processed material such as organically coated waste and organic material including: biomass, industrial waster, municipal solid waste and sludge; the method comprising placing a material to be treated in an oven having a rotatable portion comprising a treatment chamber heating the material in the treatment chamber by introducing hot gasses therein to gas inlets in at least one wall of the treatment chamber; rotating the over so as to cause the material therein to tumble; and retarding the movement of the waste material in the processing chamber by placing the retarder means in the movement path of the waste material.

As discussed above by retarding the movement of waste material in the processing chamber in this way a greater surface area to volume ratio of waste product is exposed to the hot gasses and the heated sides of the waste processing chamber.

Preferably the method further comprises agitating the material in the processing chamber by moving the retarder means between an active position, in which they protrude into the treatment chamber, and an inactive position in which they protrude into the treatment chamber by a lesser amount. Preferably the retarder means are repeatedly moved between their active position and their inactive position. This agitation of the material being processed lifts it from the surface on which it is sitting and, by agitating it, provides a constant gas path therethrough so that gas emitted from outlets in the side wall of the processing chamber on which the waste material is sitting can omit from those outlets and pass into, and through, the agitated waste material by agitating the waste material in this way a constant flow of gas is maintained through the gas outlets, even when a relatively large mass of material being processed being present in the processing chamber and located on top of those outlets.

Preferably hot gases may also be passed through flow paths in the retarder means, thereby directly delivering hot gas into the centre of the material being processed.

The method may further comprise rotating one or more of the retarder means. The introduction of hot gas directly into the centre of the waste being processed, together with the retarded movement of the waste material as the oven is rotated results in a far quicker heat transfer into the material being processed.

Method preferably further comprises moving to, and retaining in, the inactive position at least some of the retarder means while they are covered with material being processed. This is particularly advantageous with retainer means such as the inverted hook type described herein. As the retarder means are moved from their active position to their inactive position while covered with the material being processed some of the material being processed will be trapped underneath the retarder means and retained in place against the hot surfaces of the oven as the oven rotates. This again assists in rapid heat transfer into the materials as some of the material is retained against hot surfaces of the oven whereas otherwise would fall therefrom by gravity.

Specific embodiments of the invention will now be described, by way of example only, with the reference to the accompanying drawings in which:

FIG. 1 shows a rotating oven of the invention;

FIG. 2 shows a partially cut away chamber of the oven of the invention;

FIG. 3 shows a isometric view of the details of retarder means in a processing chamber of the present invention.

FIGS. 4 and 5 show the movement of the retarder means between its active and its inactive position,

FIG. 6 shows a further embodiment of the present invention; and

FIGS. 7 and 8 show diagrammatic views of the movement of material being processed within the oven as it moves both with and without retarder means being provided.

Referring to FIG. 1 a rotating oven is shown. The oven 10 comprises a processing chamber 12 and a charging box 14 attached to the processing chamber that allows the waste to be added to and removed from the oven. The principle fundamentals of the way in which this oven works can be found in prior art document WO 2004/059229. Waste material to be processed is loaded into the charging box which is then attached to the oven. The oven is rotated as the material therein is heated to cause it to break down. The material may be heated in a zero or substantially zero % oxygen environment so that is pyrolyses therein to create gas.

Although the prior art is described as having an integral afterburner to combust the gasses being produced it would be appreciated that this afterburner may be separated from the oven and connected thereto by a conduit. It will be appreciated by the skilled person that the afterburner can either act to burn the gasses produced in the chamber to produce heat that may be usable, for example, for driving a boiler. Alternatively, the afterburner could be provided with a source of fuel and a source of oxygen to burn the fuel so that the gas in the vicinity of the afterburner that has originated from the processing chamber is heated to a high temperature so as to destroy any therein but is not in fact combusted. In this way a clean fuel gas can be produced which can be, for example, combusted in a gas turbine. Various modifications to the process parameters to achieve slightly different results depending upon the exact material being processed will be apparent to the skilled person.

Referring to FIG. 2 a partial section through a processing chamber of the oven is shown. The processing chamber has a double walled construction having an outer wall 20 and an inner wall 22. The processing chamber has an open end 24 through which material may enter the processing chamber from the charging box (see FIG. 1). A plurality of retarder means 26 extends from an actuator 28 located outside the processing chamber, through the space 25 between the outer wall 20 and the inner wall 22, and protrude into the processing chamber. Although only three such retarder means are shown for clarity in reality a large number of retainer means may be used. In particular an XY array of retainer means and the retainer means may be provided on more than one side of the processing chamber. As the processing chamber is rotated the retarder means 26 slow the movement of the material 29 being processed thereby increasing its exposure to heat.

Referring to FIG. 3 more detail of the retarder means is shown. Each retarder means comprises a plurality of inverted hook elements 30 positioned in a circular array around a common central axis. The central axis forms a shaft 32 that passes through the inner wall 22 to a magnetically repelled plate 34 at the end of the shaft 32 which in turn is activated by an actuator 28 located outside the processing chamber. The actuator 28 is preferably of the magnetic type such that when energised the shaft 32 of the retainer means which is at least in part made from a porous material, will be pulled down into the actuator thereby moving the retarder means from its active position 26 a to its inactive position 26 b as depicted in FIG. 3. The inner wall 22 has clearance holds that allow the shaft 32 of the retarder means to pass there through and guide the shaft loosely as it travels between its active and inactive positions. The holes in the inner wall do not have to be gas tight as it is not problematic if a small amount of gas leaks through these holes. The inner wall 22 has a plurality of gas inlets 36 that allow hot gasses passing between the outer wall 20 and the inner wall 22 to pass therethrough into the processing chamber so as to come into direct contact with the material therein. The passage of the hot gas in the gap between the outer wall 20 and the inner wall 22 heats the inner wall 22 so that any material to be processed that is in contact with the inner wall is heated by means of conduction by the inner wall 22.

The actuator 28 may also be configured to rotate the retarder means 26 so as to agitate the material in the oven.

The inverted hooks of the retarder means 26 may be manufactured from any suitable material that is resistant to heat and which has the necessary resilience to allow it to deflect as it moves between its active position 26 a and its inactive position 26 b when the actuator 28 is activated the shaft of the retarder means is pulled into the actuator and the inverted hooks of the retarder means are pulled flat against the inner wall of the processing chamber. The retarder means can move from its inactive position to its active position by one of two means. Either the actuator 28 can be a push pull actuator and can directly move the retarder means from its inactive position 26 b to its active position 26 a or, alternatively, the resilience of the inverted hooks of the retarder means can use their natural spring force to return to their natural position thereby moving the retarder to its active position.

FIGS. 4 and 5 show an alternative arrangement of retarder means wherein the shaft 38 of the retarder means does not extend through a seal in the outer wall of the processing chamber. In the example shown in FIGS. 4 and 5 the shaft 38 terminates in a plate 40 within the space between the outer wall 20 and the inner wall 22. In this arrangement the actuator 28 is a strong electromagnet and the plate 40 and/or shaft 38 are ferrous. Activation of the electromagnet 28 pulls the plate 40 in the direction of arrow A thereby moving the retarder means 26 to its inactive position. When the electromagnet 28 is deactivated the natural resilience of the retarder means 26 moves it in the direction of arrow b into its active position. The inverter hooks 30 of the retarder means may comprise hollow tubes and the retarder means 26 may have a gas inlet 42 on the shaft 38 that extends between the outer wall 20 and the inner wall 22. Gas flowing between the two walls can therefore enter the shaft 38, pass through the inverted hooks of the retarder means 26 and exit from the ends thereof into the processing chamber.

As can be seen from the Figures the ends of the inverted hooks 30 of the retarder means are bent up so that their end is facing away from the inner wall 22 of the processing chamber ensuring that gas can pass into the material sat on top of the retarder means and not into the inner wall 22.

Referring now to FIG. 6 an embodiment is shown wherein the retarders 26 have a hinge joint 44 that is in the processing chamber when the retarder is in its active position and which is in the space 25 between the inner wall 22 and the outer wall 20 when inactive. In this way, as the retarder 26 is raised into its active position, the tips of the retarder 26 bend at its hinge 44 and the plurality of hook elements expose themselves to a grater surface area of the moving material within the chamber thereby increasing the retarding effect of the movement thereof. Activation of the electromagnet 28 creates a force on the plate 40 and moves the actuator to its inactive position. As the hinge 44 passes through the inner wall 22 it will re-orientate the retarder 26 in its original position. By hinging the retarders their inverted hooks act to catch some of the material as it tumbles and this assists in retaining the material in contact with the largest surface area of the chamber walls.

In one mode of operation, when the retarder means are covered with material that has been processed they may be moved between there active and inactive positions so as to agitate the material being processed.

In use the retarders can be moved between their active and inactive positions as the oven rotates. It will be appreciated that the sequencing of the retarders can be varied depending on the exact material being processed. However, the purpose remains the same, that is to maximise the exposure of the waste material to the incoming hot gasses and the sides of the processing chamber that become heated by the passage of the gasses thereover.

Referring to FIG. 7, generally, when an oven of the prior art rotates the material therein tends to move as a single mass as the oven rotates, that is, as the oven rotates the material does not initially move due to static friction between the material and the side of the chamber. Once the rotation reaches a certain level the static friction is overcome and, as the kinetic friction is less than the static friction the material moves across the surface of the chamber (as depicted by the arrow) as a single mass from a first position depicted by the dashed line to a second position depicted by the solid line. By moving in this way the lump of material 29 has a low surface area in contact with the walls of the chamber and there will be a large area of heated chamber wall 46 that is not in contact with the material in either position. This increases the time taken to get heat into the material and thereby increases its processing time.

Referring to FIG. 8, by using the present invention, when the gravitational pull on the material is sufficient to overcome the static friction it starts to move across the surface of the chamber. However, the retarders 26, which are in their active extended position on the surface the material is moving across slow the movement, and separate the material as it moves so that it does not all move as one mass. This has two effects. Firstly the surface area/volume ratio of the material is increased and secondly a larger amount of that area is in contact with the heated walls of the treatment chamber.

While the material is spread about the face of the treatment chamber the retarders can be retracted into their inactive position. Retracting the retarders in this way will trap a certain amount of the material being processed between the retarders and the chamber walls, thereby preventing all the material falling to the lowest point of the rotating chamber. As the chamber continues to rotate this material 29 a will be held against the wall of the chamber and, as the walls of the chamber are heated will continue to have a large surface area available to absorb heat therefrom, even on the sides of the chamber with which the majority of the material has contact.

Some materials being processed may be quite dense and their mass may be sufficient to block or partially block the flow of hot gasses into the treatment chamber from the nozzles. The retarders can, in this case, be moved between their active and their inactive positions. Moving them in this manner will move the material covering the jets and enable hot gasses from the jets to better permeate into the material. As discussed above the retarders themselves may also have hot gas passages therethrough to disperse hot gas into the material as they move. 

1. Apparatus for processing material such as organically coated waste and organic materials including biomass, industrial waste, municipal solid waste and sludge; the apparatus comprising: an oven having a rotatable portion comprising a treatment chamber adapted to receive material for treatment; a plurality of gas inlets in at least one wall of the treatment chamber through which hot gasses are introduced to the treatment chamber to heat the material therein so as to cause the organic components thereof to pyrolyse or gassify; and at least one retarder means located in the treatment chamber to retard the movement of waste material therein as the oven rotates.
 2. An apparatus according to claim 1 wherein the oven has at least one 15 substantially flat side and the retaining means are provided on the flat side of the oven.
 3. An apparatus according to claim 1 wherein the retarder means can be moved between an active position in which they protrude into the treatment chamber by a first distance and an inactive position wherein protrude into the treatment chamber by a second distance, the first distance being greater than the second distance.
 4. An apparatus according to claim 3 wherein in the inactive position the retarders are substantially flush with the walls of the treatment chamber.
 5. An apparatus according to claim 3 wherein the retarder means are made of spring steel and wherein the retarder means resiliently deforms when the retarder means is moved from its active position as in inactive position.
 6. An apparatus according to claim 3 wherein the retarder means extend through the walls of the treatment chamber and further comprise actuator means located outside the treatment chamber for actuating the retarder means.
 7. An apparatus according to claim 1 wherein the treatment chamber has a double wall, comprising an inner wall and an outer wall, extending along at least one of its sides and wherein the retarder means extend through both the inner and the outer wall.
 8. An apparatus to claim 1 wherein the retarder means further comprise a flow path there through and hot gases are introduced into the treatment chamber through the retarder means.
 9. An apparatus according to claim 7 wherein the retarder means further comprise a flow path there through and hot gases are introduced into the treatment chamber through the retarder means, the flow path having at least one flow path inlet in a section extending thereof between the inner and outer walls, and at least one outlet in a section thereof extending into the treatment chamber.
 10. An apparatus according to claim 1 wherein the retarder means each comprise a plurality of inverted hooks arranged in a radial array about a common central axis with the ends of the hooks spaced from the common central axis.
 11. An apparatus according to claim 1 wherein the retarder means each comprise at least one hollow tube through which hot gas can pass into the treatment chamber.
 12. An apparatus according to claim 10 wherein the inverted hooks each comprise a hollow tube through which hot gas can pass into the treatment chamber.
 13. An apparatus according to claim 1 wherein the retarder means can be rotated.
 14. An apparatus according to claim 12 wherein the ends of the inverted hooks are bent in a direction towards said processing chamber so that, in use, hot gas emitting from them is directed away from the surface of the treatment chamber.
 15. An apparatus according to claim 1 wherein the retarder means comprises a shaft and a retarder head, and wherein the shaft is pivotally connected to the retarder head.
 16. A method of processing material such as organically coated waste and organic materials including: biomass, industrial waste, municipal solid waste and sludge; the method comprising: placing material to be treated in an oven having a rotatable portion comprising a treatment chamber; heating the material in the treatment chamber by introducing hot gasses thereinto via gas inlets in at least one wall of the treatment chamber; rotating the oven so as to cause the material therein to tumble; and retarding the movement of the material in the processing chamber by placing retarder means in the movement path of the waste material.
 17. The method according to claim 16 further comprising agitating said material in the processing chamber by moving the retarder means from an active position in which they protrude into the treatment chamber from an inactive position wherein they protrude into the treatment chamber by a lesser amount.
 18. The method according to claim 17 comprising repeatedly moving the retarder means between their active position and their inactive position.
 19. The method according to claim 16 further comprising introducing hot gasses into the treatment chamber by passing the hot gasses through a flow path in the retarder means.
 20. The method according to claim 16 further comprising agitating said material in the processing chamber by rotating the retarder means.
 21. The method according to claim 16 further comprising moving to and retaining in their inactive position at least some of the retarder means while they are covered material being processed so as to trap in least some of the material against the wall of treatment chamber.
 22. The method according to claim 21 further comprising continuing to rotate the oven while retaining said at least some of the retarder means in their inactive position so as to retain said trapped material adjacent to the sides of the treatment chamber as the oven rotates.
 23. The method according to claim 16 comprising selectively retarding the movement of material within the treatment chamber as the chamber rotates so as to provide a greater contact area between the chamber walls and the material. 